<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes" />
    <title>ShellCheck: SC2193 – The arguments to this comparison can never be equal. Make sure your syntax is correct.</title>
    <link rel="stylesheet" href="css/bootstrap.min.css" />
  </head>
  <body style="margin-left: auto; margin-right: auto; max-width: 800px">
    <h1>SC2193 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC2193">See this page on GitHub</a>
    <p style="display: none"><a href="index.html">Sitemap</a></p>
    <hr />
    <h2
id="the-arguments-to-this-comparison-can-never-be-equal-make-sure-your-syntax-is-correct">The
arguments to this comparison can never be equal. Make sure your syntax
is correct.</h2>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC2193.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="bu">[</span> <span class="va">$var</span>+1 <span class="ot">==</span> 5 <span class="bu">]</span>              <span class="co"># Unevaluated math</span></span>
<span id="cb1-2"><a href="SC2193.html#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="bu">[</span> <span class="st">&quot;{</span><span class="va">$var</span><span class="st">}&quot;</span> <span class="ot">==</span> <span class="st">&quot;value&quot;</span> <span class="bu">]</span>      <span class="co"># Swapped around $ and {</span></span>
<span id="cb1-3"><a href="SC2193.html#cb1-3" aria-hidden="true" tabindex="-1"></a><span class="bu">[</span> <span class="st">&quot;</span><span class="va">$(</span><span class="ex">cmd1</span><span class="va">)</span><span class="st"> | cmd2&quot;</span> <span class="ot">==</span> <span class="st">&quot;42&quot;</span> <span class="bu">]</span> <span class="co"># Ended with ) too soon</span></span>
<span id="cb1-4"><a href="SC2193.html#cb1-4" aria-hidden="true" tabindex="-1"></a><span class="kw">[[</span> <span class="st">&quot;</span><span class="va">$var</span><span class="st"> &quot;</span> <span class="ot">==</span> <span class="pp">*</span>.png <span class="kw">]]</span>       <span class="co"># Trailing space</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC2193.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="bu">[</span> <span class="va">$((var</span><span class="op">+</span><span class="dv">1</span><span class="va">))</span> <span class="ot">==</span> 5 <span class="bu">]</span>          <span class="co"># Evaluated math</span></span>
<span id="cb2-2"><a href="SC2193.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="bu">[</span> <span class="st">&quot;</span><span class="va">${var}</span><span class="st">&quot;</span> <span class="ot">==</span> <span class="st">&quot;value&quot;</span> <span class="bu">]</span>      <span class="co"># Correct variable expansion</span></span>
<span id="cb2-3"><a href="SC2193.html#cb2-3" aria-hidden="true" tabindex="-1"></a><span class="bu">[</span> <span class="st">&quot;</span><span class="va">$(</span><span class="ex">cmd1</span> <span class="kw">|</span> <span class="ex">cmd2</span><span class="va">)</span><span class="st">&quot;</span> <span class="ot">==</span> <span class="st">&quot;42&quot;</span> <span class="bu">]</span> <span class="co"># Correct command substitution</span></span>
<span id="cb2-4"><a href="SC2193.html#cb2-4" aria-hidden="true" tabindex="-1"></a><span class="kw">[[</span> <span class="st">&quot;</span><span class="va">$var</span><span class="st">&quot;</span> <span class="ot">==</span> <span class="pp">*</span>.png <span class="kw">]]</span>        <span class="co"># No trailing space</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>ShellCheck has determined that the two values you're comparing can
never be equal.</p>
<p>Most of the time, this happens because of a syntax issue that
introduced unintended literal characters into one of the arguments.</p>
<p>The left-hand side in the problematic examples will always contain
(respectively) curly braces, pipe and trailing space. The right-hand
sides are literal values and a pattern without trailing spaces, so they
will never be equal. The statement is therefore useless, strongly
indicating a bug.</p>
<h3 id="exceptions">Exceptions:</h3>
<p>None.</p>
    <hr />
    <p style='font-size: 80%'><a href="../index.html">ShellCheck</a> is a static analysis tool for shell scripts. This page is part of its documentation.</p>
  </body>
</html>


